ESSENTIAL FLORAL LEAVES. 



97 



Fig. 46. —Stamen of 

 Sage. /. filament ; 

 c. connective ; If. 

 fertile anther lobe ; 

 Is. aborted anther 

 lobe. 



The anther lobes present various shapes, linear, oval, kidney- 

 shaped, &c., and they may possess tail-like appendages, as in 

 heath. One lobe may be aborted, as in sage 

 (fig. 46), while in mallow the anthers produced 

 by branching have also but one lobe, and are, 

 so to speak, half-anthers. The surface of the 

 anther may be more or less hairy, as in dead 

 nettle. When the pollen is ripe, the anthers 

 open or dehisce to liberate it. Most commonly 

 each lobe splits longitudinally, and the slit faces & 

 to the side, interior, or exterior, according as 

 the anther is innate, introrse, or extrorse. In 

 other cases, as potato and heath, a pore or minute 

 fissure is formed at the tip of each lobe. In 

 barberry the dehiscence is valvular, i.e., part of 

 the wall in each lobe becomes detached and turns 

 up as a kind of flap, which remains united to 

 the tip of the anther. 



Pollen is usually in the form of a fine sticky 

 or dry powder, composed of an immense num- 

 ber of minute pollen grains. In heath and rho- 

 dodendron several grains are united together, and in orchids the 

 whole of the pollen in each lobe of the solitary anther is agglu- 

 tinated into a club-shaped mass termed a pollinium (fig. 47). 



Stamens sometimes occur in which the anthers are absent. 

 They are then termed staminodes, and are often leaf- like. Com- 

 pare the allied forms, mullein, pentastemon, snap- 

 dragon, and foxglove (cf. p. 94). These possess, 

 respectively, five stamens, four stamens and a large 

 staminode, four perfect and one aborted stamens, 

 and four stamens. We are justified, therefore, in 

 concluding that an odd fifth stamen has been sup- 

 pressed or absolutely done away with in foxglove, 

 especially as, so to speak, there is a " vacant chair " 

 left by it. Similarly (cf. p. 93), if we take the closely fig. 47.— Poiiinia 

 related water-pimpernel and primrose, we shall find 

 that one has five perfect stamens superposed to the petals and five 

 staminodes alternating with them, the other five stamens super- 

 pose to the petals. Hence the conclusion is reached that a whorl 

 of stamens has been suppressed in primrose. Observations like 

 these, extended over a large number of cases, have led to the 

 conclusion that two whorls are typical for the andrceeium. 



Yellow is the most common colour for stamens, especially the 

 anthers, but this is by no means an invariable rule. 



Structure. — The three systems of tissue can be recognized in 



G 



